As for a housing of a discharge lamp lighting apparatus, a metal housing has been used, conventionally. It, however, is necessary to provide a clearance between the housing and a printed circuit board or to provide an insulator between them for assuring the insulation between the housing and the printed circuit board on which a discharge lamp lighting circuit is mounted, and thereby, it is difficult to downsize the discharge lamp lighting apparatus. In recent years, it is required to downsize the discharge lamp lighting apparatus and a lighting system using the same, so that a housing made of a synthetic resin, which requires no insulation between the housing and the printed circuit board and enables to downsize and to reduce the manufacturing cost, is used.
An example of a discharge lamp lighting apparatus using a housing of synthetic resin is shown in FIG. 10 and FIG. 11. As shown in FIG. 11, the housing 101 of the discharge lamp lighting apparatus 100 is formed as a rectangular solid shape which is longer in cross direction. As shown in FIG. 11, the housing 101 is comprised of a base member 102 which is formed as a tubular box shape and has a rectangular bottom plate 121 and side walls 122 set up along entire circumference of an upper face of the bottom plate 121, and a cover member 103 for closing an upper opening of the base member 102. A printed circuit board 104, on which a discharge lamp lighting circuit is mounted, is contained in an inside of the base member 102.
Wire putting grooves 123, from which electric wires 105 electrically connected to the printed circuit board 104 are put out to outside of the housing 101, are provided on both of front and rear ends of the opening of the base member 102. Wire putting grooves 133 are provided on the cover member 103 at positions corresponding to the wire putting grooves 123 of the base member 102. When the base member 102 and the cover member 103 are coupled, through-holes for communicating the inside and the outside of the housing 101 are formed. For example, since guide protrusions 135 are formed on a lower face of the cover member 103, the base member 102 and the cover member 103 are coupled by engaging the guide protrusions 135 with recesses (not illustrated) provided on inner faces of the side walls 122 of the base member 102.
Hereupon, the circumferences of the wire putting grooves 123 are necessary to be formed that mechanical strength of them are made higher than that of the other sections. In order to increase the mechanical strength, it is considered that the side walls 122 of the base member 102 in the vicinity of the wire putting grooves 123 are made thicker. However, when the side walls 122 are made thicker, it may cause the occurrence of shrinkage cavity or welding in molding, so that the method for simply making the side walls 122 thicker cannot be adopted. Therefore, in the conventional housing 101, hollow protruding portions 124 bottoms of which are opened are provided for protruding from outer peripheral faces of the side walls 122, and the wire putting grooves 123 are formed on upper faces of the protruding portions 124. Protruded portions 134 are provided on the cover member 103 at positions corresponding to the protruding portions 124, and the wire putting grooves 133 of the cover member 103 are formed on the protruding portions 134. In this way, by providing the protruding portions 124, the side walls 122 are partially configured as overlap structure, so that the mechanical strength in the vicinity of the wire pulling grooves 123 can be increased without making the side walls 122 thicker.
By the way, a die for molding the above-mentioned base member 102 needs cores for forming the inner hollow cavities of the protruding portions 124, so that the configuration of the die becomes complex and the manufacturing cost thereof becomes higher. Furthermore, each core has a height at substantially the same level as that of the side walls 122, and has substantially the same width and thickness as those of the inner hollow cavity of the protruding portion 124, so that it is wider in width and higher in height in comparison with thickness. Therefore, mechanical strength of the core is lower than that of the other portion of the die, and the core may be replaced frequently, so that the life of the die becomes shorter. As a result, it causes the increase of the costs of the discharge lamp lighting apparatus and the lighting system using the same.